1. Field of the Invention
The presently disclosed subject matter relates to lens devices and, in particular, to a lens device in which a position and size of an AF area (an AF frame) is changeable, which is a target range for auto-focusing.
2. Description of the Related Art
As an autofocus (AF) adopted in a video camera such as a broadcasting video camera, a contrast-type AF has been known. In the contrast-type AF, a subject image formed by a taking lens is obtained by an image pickup element, and the focus of the taking lens is controlled so that the contrast of the subject image is maximum.
Also, in the contrast-type AF, the entire imaging screen (imaging range) is not taken as an AF target range. In general, a rectangular part of an AF area of the imaging screen is taken as an AF target range. A technology has been conventionally known in which the position and size of the AF area on the imaging screen can be changed and a desired subject in the imaging range is brought into focus by AF (for example, refer to Japanese Patent Application Laid-Open No. 10-173980).
Meanwhile, in an imaging system such as a television camera, a lens device including a taking lens is attachable to and removable from as camera (a camera head). Generally, in such imaging system, information required for displaying various information on a view finder is collected by the camera, and a video signal is generated in a circuit in the camera by superposing various information on the imaged video and outputted to the view finder. In such imaging system, when a lens device capable of changing the position and size of an AF area (an AF frame) and a camera are mounted as described above, an imaging system is constructed as follows, for example.
A main circuit for performing AF processing is mounted on the lens device, and a signal of a subject image required for contrast-type AF (a video signal for AF) is given from the camera to the lens device. Also, an operation unit for an operator to make an instruction for the position and size of the AF frame is connected to the lens device, and the operation by the operator is accepted with this operation unit. And AF-frame information indicating the position and size of the AF frame based on the accepted operation is sent from the operation unit via the lens device to the camera. The camera accepting the AF-frame information from the lens device superposes the AF frame on the imaged video for display on the view finder.
However, while some existing cameras have a function of displaying the AF frame on the view finder, some existing camera do not have the function. While even some cameras without the function of displaying the AF frame have a function of fixedly displaying a rectangular frame similar to the AF frame at a center part of a screen of a view finder, the frame does not match the actual AF frame.
Thus, it can be thought that the camera configuring the imaging system may not have an AF-frame display function. In this case, even hen the operator operates the operation unit to change the position or size of the AF frame, the operator cannot check the AF frame on the view finder. Moreover, once the position or size of the AF frame set in advance is changed, it is also difficult to estimate at which position and which size the AF frame is set on the imaging screen.
To solve these problems, in an auto-focus system described Japanese Patent Application Laid-Open No. 2005-345605, it is determined whether a camera where a lens device capable of changing the position and size of the AF frame is mounted has the AF-frame display function. Then, when the lens device is mounted on a camera without the AF-frame display function, the AF frame is fixed at a position and size set in advance.
Furthermore, an AF area operation device described in Japanese Patent Application Laid-Open No. 2006-195342 obtains a video signal of imaged video being imaged by a camera, generates video by superposing an AF frame indicating a range of an AF area on the imaged video, and outputs a video signal of the video obtained by superposition to a view finder of the camera. With this, even if a camera without the AF-frame display function is used, the AF frame is displayed so as to be able to be recognized by the operator.